With the large scale integration of semiconductor devices, the enlargement of diameters of semiconductor wafers and the increase of areas of liquid crystal displays, the requirements of a treatment device for carrying out etching processing and film formation processing on the semiconductors become severe year by year. Also with regard to a plasma treatment device such as a plasma etching apparatus, a plasma CVD apparatus and a plasma ashing apparatus, the above situations are similar. That is to say, in order to improve a throughput, the increase of the density of plasma and the enlargement of the area of workpieces to be processed as well as the realization of cleaning have become important themes.
As plasma sources for use in the above-mentioned plasma treatment device, there are a radio-frequency capacitively coupled plasma source, a microwave ECR plasma source, a radio-frequency inductively coupled plasma source and the like, and they are used separately in treatment process to make the best use of the characteristics of each plasma source. Among these three plasma sources, plasma treatment devices provided with the radio-frequency inductively coupled plasma source have rapidly come into wide use in recent years.
One example of the inductively coupled plasma treatment device is disclosed in Japanese Patent Unexamined Publication No. 2-235332. In this inductively coupled plasma treatment device, a high-frequency electric power on the order of several hundred kHz to several hundred MHz is fed to a loop, coil, or spiral-shape antenna which is placed on the outside of the processing chamber via an insulator such as quartz forming part of the chamber, and an induced electric field formed by the antenna supplies energy to a process gas introduced into the processing chamber to generate and maintain a plasma.
There is a case of providing an antenna inside the chamber of the plasma treatment device of the radio-frequency inductively coupled plasma. For example, Japanese Patent Unexamined Publication No. 7-106095 describes a case where a spiral-shape antenna which is a RF induction coil is set up at a position facing semiconductor wafers which is a workpiece in the chamber. In these RF inductively coupled plasma treatment devices, an induction current is generated in the plasma and the plasma and the high-frequency antenna are inductively coupled in terms of electric circuit (a transformer circuit which treats the antenna as the primary coil and the current in the plasma as the secondary coil). Therefore, this is called the inductively coupled plasma treatment device.
The advantages of the plasma treatment device of the inductively coupled plasma are: (1) in a simple and low-cost construction of a simple antenna and a radio-frequency electric power source, a plasma of relatively high density of 10.sup.11 to 10.sup.12 (piece/cm.sup.3) can be generated under a low pressure of a few mTorr; (2) by arranging a coil in a planar manner facing the workpiece, a large-area plasma can be easily generated; and (3) because of the simple interior of the processing chamber, particles flying over the workpiece during processing can be reduced.
In such an inductively coupled plasma treatment device, a plasma of high density under low pressure is generated and the mean free path of ions becomes long. This makes it possible to true up the directions of ions incident upon the workpiece and a high processing rate and fine working can be obtained.